Some vehicles have water pumps that are belt driven but are clutched so as to permit the impeller of the water pump to be turned on and turned off. In some more advanced proposed united, the clutch may be cycled on and off repeatedly according to an adjustable duty cycle, permitting the water pump to achieve a range of selected flow rates for the coolant in the vehicle's coolant system. While such proposed units are advantageous it would be beneficial to be able to determine if there is a breakdown in the water pump that causes is to be non-operational (e.g. not pumping at all), or that causes it to be stuck at full flow. Furthermore, it would be beneficial to be able to determine the speed of the water pump when it is operating. Preferably one or more of these features can be provided at relatively low cost.